Like everything else it depends.......
Do you want that new camera right now?
The D7000 is a very nice camera but it has some (to me) annoying features. The annoying features are the shooting styles. You get those in the D90 too. In the D300 and presumably in the D400, you will not have those. If Nikon follows their past procedure, the D400 will differ from the D7000 in having a more robust build. It will be a bit larger and heavier. It will also have more focus points and maybe an ability to shoot photos in rapid succession faster. If I were you, I would compare the specs on the D300s and the D90. Those differences should give you are pretty good idea of what to expect in the D7000.
That being said, Nikon is going to take their own sweet time in releasing a D400. I would think that it would come out this year. But that is a guess on my part. If the D300s kind of features are important to you and you don't mind waiting an indefinite period of time, then by all means wait for the D400. However, the D7000 is regarded as a very good camera and you would probably be quite happy with it.
Of course, you could just go whole hog and get the D800.